Using eight established immunohistochemical markers to assess the status of the DDR machinery, we found pronounced endogenous DNA damage signalling (γH2AX marker) and robust constitutive activation of both the ATM‐Chk2 and ATR‐Chk1 DNA damage checkpoint kinase cascades, yet unexpectedly modest p53 tumour suppressor activation, across our medulloblastoma cohort. Here, CHEK1 is linked to medulloblastoma.